You are very brave Ed ! I've never done any metal shaping except for spinning copper over a wooden core (buck?) on a lathe and then finish it with a hammer. It would be scary to do a hunk of sheet metal as big as you're doing !
Heres a pic of the copper cover I made to fit over the ships compass on my binnacle that came off a Japanese cargo ship sunk over in Kwajalan Island in 1944......Bruce